Byrd, 34, has publicly acknowledged a post-BALCO working relationship with Victor Conte, whose California lab became the epicenter of the largest doping scandal in North American sports history.

Byrd said in a statement released by the players' union that he took tamoxifen due to side effects from an unspecified surgery. He told USA TODAY Sports' Bob Nightengale in a text message: "I do want to say that Victor had nothing to do with this. He didn't know about me taking tamoxifen or the positive test until two days ago."

"I feel bad for Marlon. He's a good guy, and now he's going to have to live with this,'' Conte said in a telephone interview. "I knew nothing about it until two days ago. But I'm the one getting slammed under the bus. It's like I'm the bad guy.

"I just feel bad for Marlon, and I certainly don't want to pile on.''

In a statement released by baseball's players' union, Byrd said he made an "inexcusable mistake."

"Several years ago, I had surgery for a condition that was private and unrelated to baseball. Last winter, I suffered a recurrence of that condition and I was provided with a medication that resulted in my positive test. Although that medication is on the banned list, I absolutely did not use it for performance enhancement reasons. I am mortified by my carelessness and I apologize to everyone who loves this game as I do. I will serve my suspension, continue to work hard and hope that I am given an opportunity to help a Club win later this season."

Tamoxifen is most commonly used for breast cancer treatment in early and advanced stages in men and women.

Byrd batted .210 (30 for 143) with one home run in stints with the Boston Red Sox and Chicago Cubs this season; the Cubs traded him to the Red Sox on April 21 and he was released by the Red Sox on June 12. He is an11-year major league veteran who hit a career-high 20 homers in 2009 for the Texas Rangers.

Byrd is the second player to have his positive test announced after MLB and the players' union agreed earlier this month to reveal the substance for which a player tested positive. Last week, the Philadelphia Phillies' Freddy Galvis tested positive for clostebol, a synthetic steroid.

To report corrections and clarifications, contact Standards Editor Brent Jones. For publication consideration in the newspaper, send comments to letters@usatoday.com. Include name, phone number, city and state for verification. To view our corrections, go to corrections.usatoday.com.

USA TODAY is now using Facebook Comments on our stories and blog posts to provide an enhanced user experience. To post a comment, log into Facebook and then "Add" your comment. To report spam or abuse, click the "X" in the upper right corner of the comment box. To find out more, read the FAQ and Conversation Guidelines.

About Daily Pitch

Daily Pitch is a baseball fan's destination for breaking news, emerging trends and enlightening banter. With a veteran group of reporters positioned in three time zones, we provide a balanced, comprehensive glimpse at our national pastime, with a nod to both the passion and complexities that make the sport irresistible to many. More about our reporters